Modern fabric comprises synthetic materials (e.g., Dacron), natural fibers (e.g., cotton), as well as blends thereof, however many skilled in the laundry art consider fabric to have two embodiments: white fabric and colored fabric. The consumer has long recognized the need to delineate between colored and white clothing. It was the common "wash-day" observation that many colored fabrics had a propensity to "bleed" into the laundry liquor and deposit onto other fabrics that led to the practice of sorting clothes into white fabric and colored fabric. In addition, because of problems with color fading, dyed fabric can not be laundered at the hotter water temperatures typical for whites. Once sorting became a standard practice within the laundry art, separate processes and materials evolved for cleaning these separated white and dyed fabric. The introduction of hypochlorite bleach into the laundry process, because it is not compatible with many fabric dyes, solidified the establishment of white and dyed material as the two major laundry categories.
Hypochlorites are among the most commonly used bleaching agents used to clean white, non-dyed fabrics. These bleaches chemically destroy the colored stains present on white fabric. It is generally regarded that for highly conjugated, fixed stains, the first treatment with bleaching agents oxidizes the stain-producing molecules to a non-colored or less colored species that is subsequently removed in the rinse cycle. For more difficult stains, further treatment with bleach is necessary, although the over usage of bleach can damage even white fabric. The goal of imparting a "bright whiteness" to white fabric has led to the development of many adjunct laundry ingredients. One such material is optical brighteners added to reduce the yellow cast that develops on white fabrics after successive washings.
Many synthetic fabrics have optical brighteners built into the fibers or fixed onto the synthetic fabric during manufacture. These additional brightening agents help to compensate in part for the yellow cast that develops when non-colored fabrics are washed in water containing heavy metal ions. However despite the use of bleaches, the incorporation of brighteners into the fabric, and other whiteness enhancing materials, some level of dinginess still persists on many white fabrics after several washings.
For colored fabrics a different set of principles exists. Although dyed and white fabrics often comprise the same natural or synthetic materials, many of the dyes used to color fabrics are susceptible to the harsh bleaching conditions used to "whiten" non-dyed fabrics. The desire to remove stains from dyed fabric has provided further impetus for the development of separate non-damaging bleaching materials for colored fabrics. However, safe stain removal is only one issue that is connected to colored fabrics. Colored materials must be guarded against fading, a condition where the original color is lost due to one or more conditions. The problems of fading, change in color intensity, or color hue are even more perceptible than the "yellowing" of whites. In fact, consumers are well aware that garments comprising different synthetic materials, but having the same color, may fade at different rates in the laundry process.
Surprisingly, the materials disclosed in the present invention provide for increased color protection for both white and colored fabrics. The dinginess and yellow cast that develops on white fabrics is reduced while the color fading and changing of color-hue of dyed fabrics are marginalized.
Without wishing to be limited by theory, the modified polyamines of the present invention are believed to serve to chelate heavy metal ions in the laundry liquor, that contribute significantly to both the yellowing of white fabrics and the fading or change of hue of colored materials. It has now been discovered that what appears to be a "washing out" of dye molecules during the wash cycle is actually in some cases a dye molecule modification process. Heavy metal ions, such as copper, chelate with dye molecules creating a perturbation and change in the absorption spectrum of these molecules. Although by this process no dye molecules are lost, the result of this chelation is a change of hue or a dimming or loss of intensity to the color of the fabric. Preventing the association of these heavy metal ions to the fabric dye molecules results in a reduction of fabric hue changing or color fading.
Conventional chelants have long been used to modify the effects of heavy metal ions in the laundry wash liquor, however these conventional chelants are removed with the bulk of the other detergent components as the laundry liquor is drained away prior to the rinse cycle. Hence, any protection afforded by these standard laundry chelants is largely lost when the wash liquor is replaced by the new rinse water which may now contain a fresh supply of heavy metals. The heavy metal chelants of the present invention are highly substantive and during the wash cycle are deposited onto fabrics from the laundry liquor. They are then slowly released during subsequent exposures to laundry cycles, for example, the following rinse cycle. For this reason they are present in all the cycles during the laundering process to protect against the effects of heavy metal ions. In fact, the substantivity of the compounds of the present invention provides protection to white and colored fabrics for several ashes after treatment with these materials has been suspended. Other types of chelants that may be used in the wash that do not have this substantive effect are much less effective against the loss and fading of fabric color quality.
The surprisingly effective compounds of the present invention are modified polyamines, especially polyalkyleneimines, that have less than 100% of their nitrogen moieties modified, that is about 0.5% to 90% of their nitrogen moieties modified. The modifying groups are polyalkoxylates such as ethoxylates or carboxylate-related moieties.
The compounds of the present invention that are modified by attachment of polyalkoxylate moieties to the polyamines are in general highly effective against the heavy metal ions responsible for color fidelity problems (e.g., copper), while the polyamines of the present invention modified for use by attachment of carboxylate moieties are superior in their protection against ions (e.g., manganese) that effect the dinginess of white fabrics and in addition are still highly effective against heavy metals responsible for color fidelity problems.